1. Field of the Invention
The present invention relates to a multi-resolution roofshooter printhead which comprises at least two arrays of printhead nozzles, each having a resolution (dot per inch or DPI) that differs from the other to provide the capability of printing draft or letter quality, or producing superior grey scale reproduction with a single printhead without complicated controls or electronics to change drop size.
2. Description of Related Art
There are two general configurations for thermal ink jet drop on demand printheads. In one configuration, droplets are propelled from nozzles in a direction parallel to the flow of ink in ink channels and parallel to the surface of bubble generating heating elements of the printhead, such as that disclosed in U.S. Pat. No. 4,601,777 to Hawkins et al. This is referred to as a "side shooter". The other type propels droplets from nozzles in a direction normal to the surface of the bubble generating heating elements, such as U.S. Pat. Nos. 4,789,425 and 4,985,710 to Drake et al (the disclosures of which are herein incorporated by reference). This is sometimes referred to as a "roofshooter".
In roofshooters, and in ink jets in general, it has been customary to provide a single array of nozzles for reproducing an image. The use of a single array is limited since the resolution is constant or requires complex circuitry to change or modify the resolution. Printers are known which provide more than one array of nozzles in a printhead, but these have been designed specifically for increasing printhead speed in reproduction. There are many needs for the ability to change resolution of a printer to provide quality reproduction of various information which may be text or graphics, black and white, grey scale or full color.
U.S. Pat. No. 4,835,551 to Ng discloses an optical recording apparatus having plural resolution recordings wherein text and graphics can be printed at two different resolutions. A control unit adjusts resolution depending on what type of image is present. This apparatus includes a plurality of recording elements (LED's) arranged in a row along the length of a printhead. Image information comprising text and characters not in an area determined to include pictorial information is reproduced at a resolution of N.times.M dots per square inch. Image information in an area including pictorial information is reproduced at a resolution of N.times.(L.times.M) dots per square inch where L is a number greater than one. This apparatus utilizes only one row of printing elements and utilizes control means (circuitry) for providing the different resolutions of the one row of printing elements by adjusting the current which is applied to drivers associated with the LED's and LED on-time duration.
U.S. Pat. No. 4,521,814 to Ono et al. discloses a method and apparatus for simultaneously outputting a graphic signal and an alphanumeric signal by using an image reproducing system. This is done using a literal head and a graphic head which have a respective number and diameter of beam components which are laser beams exiting from the respective heads. This reference describes methods to synchronize the pitches of the two heads.
U.S Pat. No. 4,789,425 to Drake et al., assigned to Xerox Corporation, discloses a fabrication process for manufacturing a roofshooter printhead. The printhead utilizes a single ink supply and an array of nozzles. Alternatively, in another embodiment, two arrays are shown for each elongated fill hole, each being offset from the other and having its own ink channels and separate ink cavity. The double array can either double linear nozzle density when the arrays are offset or double printing speed when the arrays are aligned.
U.S. Pat. No. 4,963,882 to Hickman discloses printing of pixel locations by an ink jet printer using multiple nozzles for each pixel wherein a nozzle failure will have a limited impact on image resolution. A pixel may be printed using two nozzles to increase resolution. Additionally, two nozzles may be used to print color images.
U.S. Pat. No. 4,550,323 to Gamblin discloses an elongated fluid jet printing apparatus wherein enhanced printer resolution is attained by a lesser density of electrodes. Two electrodes drive a single nozzle. Alternatively, in another embodiment, a double array of nozzles having an electrode on each end is disclosed. This reference also is deficient for failing to teach or suggest the use of multiple arrays, each having a different resolution.
U.S. Pat. No. 4,692,773 to Saito et al. discloses an image forming method using image forming elements having different concentrations and pitches wherein a forming element is driven with a varying signal which varies the size of a dot produced by the element.
U.S. Pat. No. 4,985,710 to Drake et al., assigned to Xerox Corporation, discloses a roofshooter printhead. Each printhead has a single ink supply and an array of nozzles.
No suggestion or teaching is present which combines in a printer the use of plural arrays of printheads, each having a different resolution. None of the known existing printing systems combine the use of multiple arrays of linear printhead nozzles, each having a different resolution to provide a simple printhead construction which is capable of providing a draft quality print and a letter quality print having different resolutions without complicated circuitry to change droplet size.
Further, the prior art does not teach or suggest a printer which is capable of providing enhanced reproduction capabilities through the use of multiple arrays of printheads, each having a different resolution which can provide multiple modes of resolution and can be utilized together to provide certain grey scale reproductions.